National Institute of Technology, Karnataka

About: National Institute of Technology, Karnataka is a education organization based out in Mangalore, Karnataka, India. It is known for research contribution in the topics: Corrosion & Cloud computing. The organization has 5017 authors who have published 7057 publications receiving 70367 citations.

Design and Implementation of Sensorless Voltage Control of Front-End Rectifier for Power Quality Improvement in Telecom System

Abstract: In this paper, a three-phase three-switch three-level boost (Vienna) type pulse-width modulation rectifier is proposed as an active front-end power factor correction (PFC) rectifier for power quality improvement in telecom load. A sensorless voltage control technique is proposed and it does not rely on any input voltage information results in reliable and robust operation. A brief description on the principle of operation and the most advantageous modulation method of the proposed system are discussed. The feasible switching states are identified for the proposed active front-end converter resulting in reduced switching stress and dc ripples. A triangular carrier based control logic is applied and the input current reaches sinusoidal shape without the need of sensing the input voltage. The detailed analysis of front-end PFC converter is carried out by equivalent circuit analysis. Also, the complete loss and efficiency calculation of the converter is explicitly carried out with the help of hardware design guidelines. The performance of the proposed system and its capability of operating satisfactorily in the event of failure of one phase of the mains is verified through MATLAB Simulation, and the results obtained are presented. The experimental setup rated for 9 kW is developed in the laboratory to validate the simulation results. From the simulation and hardware results, it is observed and recorded that the power quality parameters are improved and are well within the IEEE and IEC standards.

Thermal and optical properties of BaO-CaF 2 -P 2 O 5 glasses

Abstract: Thermal and optical properties of ternary phosphate glasses prepared by conventional melt-quenching technique, belonging to the series (50 − X)BaO–XCaF 2 –50P 2 O 5 (X = 0 to 10 mol%) were investigated with increase in CaF 2 content. Thermal stability and glass forming ability studied using differential thermal analysis (DTA) were found to increase with the increase in CaF 2 content. Powder X-ray diffraction (XRD) analysis of heat treated samples also revealed that CaF 2 addition improves the thermal stability against crystallization. Increase in both glass transition temperature and onset crystallization temperature with the increase in CaF 2 content can be attributed to the partial substitution of Ba 2 + ion with Ca 2 + ion, which is having larger field strength. The observed decrease in the melting temperature of glass batch with the increase in CaF 2 content indicates that CaF 2 acts as a flux and reduces the viscosity of the glass melt. The decrease in refractive index of the glasses with the increase in CaF 2 content can be attributed to replacement of lower field strength Ba 2 + by Ca 2 + or the partial substitution of more polarizable oxygen ion by fluorine. Optical band gap energy slightly increased and Urbach energy marginally reduced with the increase in CaF 2 content. Increase in optical band gap energy was further confirmed by calculating theoretical optical basicity of glasses. Average anion polarizability (α O/F ) of (50 − X)BaO–XCaF 2 –50P 2 O 5 glasses calculated from refractivity data using Lorentz–Lorentz relation was correlated with its theoretical optical basicity (λ th ) using the previously established correlation for oxyfluoro phosphate glasses.